Thermodynamic Calculation on the Formation of Titanium Hydride

从钛氢化物的组成元素的基本性质出发,利用修正的Miedema生成热模型,对TiHx (1≤x≤2)的标准焓变行了计算. 采用量子力学和统计热力学的方法,计算出了TiH2的振动和电子熵,提出了一种计算TiH2标准熵变的方法. 结果表明,TiHx的标准焓变值随着x的增加呈线性关系减少. 计算得到的TiH2在298.16 K时的标准焓变值、标准熵变值以及吉布斯自由能分别为-142.39 kJ/mol、-143.08 J/(mol?K)和-99.75 kJ/mol. 计算结果与文献中实验或理论计算得到的结果均符合较好,表明所提出的钛氢化物的热力学模型是可行的.     

基于Pro／E和ADAMS的阀门气动执行器仿真优化

以阀门气动执行器为研究对象,运用三维设计软件Pro／E构建实体模型,并实现虚拟装配。利用Pro／E和ADAMS的接口软件Mech／Pro,将模型导入到ADAMS／View下并建立完整的虚拟样机模型,对模型进行动力学仿真分析。利用ADAMS／View的设计研究功能,对机构进行优化设计．得到了使阀门气动执行器运动较为平稳的活塞杆尺寸参数。     

基于UML的任务规划系统建模与设计

任务规划系统是提供辅助决策的一种科学而有效的手段。由于系统包含要素的开放性和复杂性特点,需要采用面向对象的分析与设计方法进行建模。UML建模技术提供了一种比较好的解决方法。通过UML建模,能够清晰描述系统的需求、功能、要素、组成、内部关系等,致使仿真软件的扩充性与重用性好,且开发效率高。本文描述了任务规划系统的用例视图、类视图和动态建模,并讨论了作战任务的描述方法和想定建模。     

Modeling of an insurance system and its large deviations analysis

We model an insurance system consisting of one insurance company and one reinsurance company as a stochastic process in R². The claim sizes {X_i} are an iid sequence with light tails. The interarrival times {τ_i} between claims are also iid and exponentially distributed. There is a fixed premium rate c₁ that the customers pay; c<c₁ of this rate goes to the reinsurance company. If a claim size is greater than R the reinsurance company pays for the claim. We study the bankruptcy of this system before it is able to handle N number of claims. It is assumed that each company has initial reserves that grow linearly in N and that the reinsurance company has a larger reserve than the insurance company. If c and c₁ are chosen appropriately, the probability of bankruptcy decays exponentially in N. We use large deviations (LD) analysis to compute the exponential decay rate and approximate the bankruptcy probability. We find that the LD analysis of the system decouples: the LD decay rate γ of the system is the minimum of the LD decay rates of the companies when they are considered independently and separately. An analytical and numerical study of γ as a function of (c,R) is carried out.     

A survey of variants and extensions of the resource-constrained project scheduling problem

The resource-constrained project scheduling problem (RCPSP) consists of activities that must be scheduled subject to precedence and resource constraints such that the makespan is minimized. It has become a well-known standard problem in the context of project scheduling which has attracted numerous researchers who developed both exact and heuristic scheduling procedures. However, it is a rather basic model with assumptions that are too restrictive for many practical applications. Consequently, various extensions of the basic RCPSP have been developed. This paper gives an overview over these extensions. The extensions are classified according to the structure of the RCPSP. We summarize generalizations of the activity concept, of the precedence relations and of the resource constraints. Alternative objectives and approaches for scheduling multiple projects are discussed as well. In addition to popular variants and extensions such as multiple modes, minimal and maximal time lags, and net present value-based objectives, the paper also provides a survey of many less known concepts.     

A systematic procedure to evaluate an automobile manufacturer–distributor partnership

Automobile manufacturer–distributor partnerships are fundamental to the success of automobile companies. The complexity of the overall partnership model often causes difficulties in partnership study. This paper presents a systematic procedure to evaluate an automobile manufacturer–distributor partnership consisting of a large number of system variables. Firstly, Interpretive Structure Modeling (ISM) is used to sort system variables into groups of various characteristics. This sorting process provides an effective means to develop a three-stage hierarchic/network model of the partnership, including Stage I: partnership selection, Stage II: partnership establishment, and Stage III: partnership maintenance. Secondly, Analytic Hierarchy Process (AHP)/Analytic Network Process (ANP) are applied to partnership evaluation based on as many as 20 system variables. Relative importance weight of all variables is quantitatively determined. The most investment-worthy variables found are management strength and power. Finally, this paper makes a comparison between the optimum distributors identified by the present procedure and in practical cases. The usefulness and efficiency of the proposed procedure are ascertained with highly consistent results in the comparison.     

A study about the existence of the leverage effect in stochastic volatility models

The empirical relationship between the return of an asset and the volatility of the asset has been well documented in the financial literature. Named the leverage effect or sometimes risk-premium effect, it is observed in real data that, when the return of the asset decreases, the volatility increases and vice versa.Consequently, it is important to demonstrate that any formulated model for the asset price is capable of generating this effect observed in practice. Furthermore, we need to understand the conditions on the parameters present in the model that guarantee the apparition of the leverage effect.In this paper we analyze two general specifications of stochastic volatility models and their capability of generating the perceived leverage effect. We derive conditions for the apparition of leverage effect in both of these stochastic volatility models. We exemplify using stochastic volatility models used in practice and we explicitly state the conditions for the existence of the leverage effect in these examples.     

Comparison of gas-phase mechanisms applied to RDX combustion model

Two detailed gas-phase chemical mechanisms for RDX – Yetter and coworkers, herein ‘Y2’ [K. Prasad, R.A. Yetter, M.D. Smooke, Combust. Sci. Technol. 124 (1997) p. 35.]; Cal. Tech. group, herein ‘CTM’ [(a) A.D. Chakraborty, R.P. Muller, S. Dasgupta, W.A. Goddard, III, J. Phys. Chem. A 104 (2000) 2261. (b) D. Chakraborty, R.P. Muller, S. Dasgupta, W.A. Goddard, III, J. Comput. Aided Mater. Des. 8 (2001) 203. (c) D. Chakraborty, R.P. Muller, S. Dasgupta, W.A. Goddard, III, Available from: http://www.wag.caltech.edu/home/rpm/projects/hedm/] – have been tested using a recently developed combustion model. The results are compared with each other and experimental data. Burning rates predicted using CTM are about 15% higher than Y2, but both compare well with experimental data across a wide pressure range. Also, majority species profiles are in reasonable agreement with data from a 0.5 atm pressure experiment. However, comparison of predicted trace species profiles to experiments indicates neither mechanism reproduces all measured trace species well; furthermore, most of these trace species occur along main reaction pathways. Detailed chemical analysis indicates the main initial RDX reaction is surprisingly very different for the two mechanisms. NO₂ scission dominates using Y2, but HONO elimination dominates using CTM, in spite of the NO₂ scission reaction having by far the largest RDX decomposition rate coefficient in each mechanism. Analysis shows the unexpected result using CTM is due to a curious global kinetics phenomenon arising in the product pathway: the ring-opening reaction, RDXR → RDXRO, where RDXR is the cyclic radical formed upon NO₂ scission, has a much smaller rate coefficient in CTM compared to Y2. This causes the reaction to be a bottleneck, and so the NO₂ scission reaction goes into partial equilibrium rather than being forwards. Tests were performed to see how the predicted burning rates would be affected by changes in some of the most sensitive rate parameters. Some of the key parameters leading to the differing predictions have been identified. These results will help guide future efforts to understand and develop an accurate representation of the actual RDX combustion chemistry.     

基于VRML的虚拟管网漫游系统的研究与实现

通过对虚拟现实技术的研究,探索一条适合于互联网上进行管网虚拟漫游系统的开发方法和手段,为管网系统的安全管理,设计决策以及虚拟教学提供一种直观、有效的方法。     

Novel multistage solid–liquid circulating fluidized bed: Hydrodynamic characteristics

The present work proposes a novel radially cross-flow multistage solid–liquid circulating fluidized bed (SLCFB). The SLCFB primarily consists of a single multistage column (having an inner diameter of 100 mm and length of 1.40 m), which is divided into two sections wherein both the steps of utilization or loading (e.g., adsorption and catalytic reaction) and regeneration of the solid phase can be carried out simultaneously in continuous mode. The hydrodynamic characteristics were studied using ion exchange resin as the solid phase and water as the fluidizing medium. The loading and flooding states were determined for three particle sizes; i.e., 0.30, 0.42, and 0.61 mm. The effects of the superficial liquid velocity and solid feed rate on the solid hold-up were investigated under loading and flooding conditions. The solid hold-up increases with an increase in the solid feed rate and decreases with an increase in the superficial liquid velocity. An artificial-intelligence formalism, namely the multilayer perceptron neural network (MLPNN), was employed for the prediction of the solid hold-up. The input space of MLPNN-based model consists of four parameters, representing operating and system parameters of the proposed SLCFB. The developed MLPNN-based model has excellent prediction accuracy and generalization capability.